This invention relates to coatings and more particularly to coatings on surfaces that are subjected to friction or wear and to coatings for tools utilized for cutting, forming and grinding.
In the past, tools have been fabricated to achieve various hardness, lubricity and wear characteristics by controlling certain parameters. For example, tools for working and shaping unhardened steels may be fabricated from steel containing enough carbon to form very hard martensite. In more complicated compositions, varying the carbon content and alloy content makes possible non-deforming steels, shock-resistant steels, hot-work steels, or high-speed steels. In some of these steels, alloying elements such as titanium, vanadium, molybdenum, tungsten and chromium are used. These are elements which have a great affinity for carbon and form hard, wear resistant metallic carbides.
Tools are also constructed of materials such as tungsten carbide and other cemented carbides.
In many cases, it is desirable to provide for such tools a coating on the surface thereof to improve the hardness and/or lubricity of the tool. This is especially the case where it is desired to lengthen the tool life or where it is necessary to shape and work hardened steel.
Types of wear resistant coatings are known. However, many types of wear resistant coatings require high temperatures for application, thereby making them impractical for use on many types of substrate materials, since the properties of the substrate may change significantly under such temperatures. Other types of coatings do not adhere well enough to the substrate under working conditions for practical use. As a result, fracture, crumbling and/or delamination of the coating can occur resulting in premature failure.
Thus, a need exists for wear resistant coatings that can be applied at relatively low temperatures to avoid significant change of substrate properties. A need also exists for wear resistant coatings for articles such as tools to provide improved properties of hardness and lubricity thereby resulting in longer tool life and an improved surface finish of parts machined therewith. Further, a need also exists to provide wear resistant coatings that have good adherence to provide resistance to fracturing, delaminating and crumbling, allowing such coatings to have more widespread use.